We ended up cutting it right over the torsion bar crossmember as suggested. The rear portion dropped right in. Fits like a glove. The front portion needed to be trimmed along the side a bit. We trimmed starting 1/4 inch from the sides, then back to where the floor levels off. This cut was a wedge so it started at the front and thinned out as it went back.
Problem now is of course the firewall. I'm going to either get a cut out from a junk yard car or make a tunnel extension to cover span the gap from the new tunnel to the firewall.
